Three‐dimensional microstructure of samples recovered from asteroid 25143 Itokawa: Comparison with LL5 and LL6 chondrite particles     

Akira Tsuchiyama  Masayuki Uesugi  Kentaro Uesugi  Tsukasa Nakano  Ryo Noguchi  Toru Matsumoto  Junya Matsuno  Takashi Nagano  Yuta Imai  Akira Shimada  Akihisa Takeuchi  Yoshio Suzuki  Tomoki Nakamura  Takaaki Noguchi  Masanao Abe  Toru Yada  Akio Fujimura 《Meteoritics & planetary science》2014,49(2):172-187

In this study, the three‐dimensional (3‐D) microstructure of 48 Itokawa regolith particles was examined by synchrotron microtomography at SPring‐8 during the preliminary examination of Hayabusa samples. Moreover, the 3‐D microstructure of particles collected from two LL6 chondrites (Ensisheim and Kilabo meteorites) and an LL5 chondrite (Tuxtuac meteorite) was investigated by the same method for comparison. The modal abundances of minerals, especially olivine, bulk density, porosity, and grain size are similar in all samples, including voids and cracks. These results show that the Itokawa particles, which are surface materials from the S‐type asteroid Itokawa, are consistent with the LL chondrite materials in terms of not only elemental and isotopic composition of the minerals but also 3‐D microstructure. However, we could not determine whether the Itokawa particles are purely LL5, LL6, or a mixture of the two. No difference between the particles collected from Rooms A and B of the sample chamber, corresponding to the sampling sequence of the spacecraft's second and first touchdowns, respectively, was detected because of the statistically small amount of particles from Room B.  相似文献   

Crystallization temperature determination of Itokawa particles by plagioclase thermometry with X‐ray diffraction data obtained by a high‐resolution synchrotron Gandolfi camera     

Masahiko Tanaka  Tomoki Nakamura  Takaaki Noguchi  Aiko Nakato  Hatsumi Ishida  Toru Yada  Kei Shirai  Akio Fujimura  Yukihiro Ishibashi  Masanao Abe  Tatsuaki Okada  Munetaka Ueno  Toshifumi Mukai 《Meteoritics & planetary science》2014,49(2):237-244

The crystallization temperatures of Itokawa surface particles recovered by the space probe Hayabusa were estimated by a plagioclase geothermometer using sodic plagioclase triclinicity. The Δ131‐index required for the thermometer, which is the difference in X‐ray diffraction peak positions between the 131 and 11 reflections of plagioclase, was obtained by a high‐resolution synchrotron Gandolfi camera developed for the third generation synchrotron radiation beamline, BL15XU at SPring‐8. Crystallization temperatures were successfully determined from the Δ131‐indices for four particles. The observed plagioclase crystallization temperatures were in a range from 655 to 660 °C. The temperatures indicate crystallization temperatures of plagioclases in the process of prograde metamorphism before the peak metamorphic stage.  相似文献   

Formation of giant low surface brightness galaxies through disc instability     

Masafumi Noguchi 《Monthly notices of the Royal Astronomical Society》2001,328(2):353-358

It is shown that the giant low surface brightness galaxies (GLSBs), characterized by a large but diffuse disc component, can result from ordinary spiral galaxies through dynamical evolution. Numerical simulations indicate that the formation of a bar in a gravitationally unstable disc with high surface density induces non-circular motions and radial mixing of disc matter, leading to the flattening of the disc density profile. The resulting decrease in the disc central surface brightness is ∼1.5 magnitude, while the disc scalelength is nearly doubled, transforming a typical high surface brightness galaxy to a GSLB. This scenario seems promising especially for the GSLBs possessing a significant bulge, which are difficult to incorporate into the traditional Hubble sequence. Namely, because this disc transmutation can operate even if a moderate bulge component exists, the GSLBs with a bulge are argued to have resulted from the high surface brightness galaxies which had already possessed a bulge. The current picture naturally explains other observed characteristics of the GSLBs as well, including the propensity for having grand-design spiral arms and a bar, a high incidence of active nuclei, and galaxy environments.  相似文献   

A Flexible Prism used as an Image Stabilizer     

T. Sakurai  M. Noguchi  K. Shinoda  N. Tanaka  K. Aoki  M. Hagino  H. Mochizuki 《Solar physics》2002,205(1):201-208

An image stabilizer was constructed by making use of a flexible prism, which is widely used as an anti-vibration mechanism in handheld video cameras. The prism responds to frequencies up to 20 Hz, and can be simply inserted into existing optics. The performance of the prism has been confirmed by observing the Sun through it.  相似文献   

IV-1 The random wave input generation system using secondary excited induction generator     

Naoki Ando  Kouhei Ohnishi  Kunio Miyachi 《Ocean Engineering》1985,12(6):573-574

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Gas flow in a two component galactic disk     

M. Noguchi  I. Shlosman 《Astrophysics and Space Science》1994,216(1-2):347-351

Numerical simulations of two-component (stars + gas) self-gravitating galactic disks show that the interstellar gas can significantly affect the dynamical evolution of the disk even if its mass fraction (relative to the total galaxy mass) is as low as several percent. Aided by efficient energy dissipation, the gas becomes gravitationally unstable onlocal scale and forms massive clumps. Gravitational scattering of stars by these clumps leads to suppression of bar instability usually seen in heavy stellar disks. In this case, gas inflow towards the galactic center is driven by dynamical friction which gas clumps suffer instead of bar forcing.  相似文献   

Note on the Kuroshio meander     

Kunio Rikiishi 《Journal of Oceanography》1974,30(1):42-45

Surface current measurements with GEK during the period from 1960 to 1962 in the region south of Japan have been analyzed statistically. Characteristics of the meander for the west of 138?E are found to be different from those for the east: the surface current speed is higher and the current path is more stable in the west of 138?E.  相似文献   

Three-Dimensional Particle Acceleration in Electromagnetic Cylinder and Torus     

Koichi Noguchi  Edison Liang 《Astrophysics and Space Science》2007,307(1-3):305-308

Particle acceleration via Poynting vector with toroidal magnetic field is studied in 3D PIC simulation of electron-positron plasma. We choose two different initial magnetic field configurations to compare how the particle acceleration is affected by the expansion of electromagnetic wave. In the cylindrical case, the electromagnetic field strength decays as (ct)⁻², and particles are accelerated in the radial direction as well as the axial direction. Rayleigh-Taylor instability is also observed at the center of the cylinder. In the torus case, the field strength decays as (ct)⁻³, making the acceleration less efficient. Particles accelerated in the axial direction by E × B force creates strong charge separation.  相似文献   

Crustal strain observation for nine years with a laser strainmeter in Kobe, Japan     

Shuzo Takemoto  Takeyasu Yamamoto  Atsushi Mukai  Shigeaki Otsuka  Kunio Fujimori 《Journal of Geodynamics》2003,35(4-5):483-498

We carried out precise crustal strain observation using a laser strainmeter system at the Rokko-Takao station in Kobe, Japan from 1989 to 1997. The long-term strain record is characterized by remarkable annual changes of the order of 2–3×10⁻⁶ and linear strain accumulation of −4.4×10⁻⁷/year (in contraction). The annual strain changes are inversely proportional to temperature changes that precede the strain changes by about 1 month. The apparent annual strain changes were mainly caused by refractive-index changes in the light path due to the ambient temperature changes. After eliminating the annual temperature effect, linear strain accumulation is corrected to be −6.3−6.7×10⁻⁷/year. Residual strains show the oscillating behavior, in which the oscillating cycle seems to become shorter and shorter as time goes by. During the period, a destructive earthquake of M=7.2 occurred near the Kobe City on 17 January 1995. We investigated the oscillating behavior in secular variations of ground-strains by introducing the deterministic approach of earthquake prediction to search for the “critical point” of the occurrence of an earthquake in the extended power law equation. However, we could not obtain a unique solution to determine eight unknown parameters including the “critical point”. This may be mainly due to lack of data for 4 months from August to November in 1994 by the failure of the laser source before the occurrence of earthquake on 17 January 1995. After removing environmental effects and tidal components, we carefully re-examined strain changes in 7 days and 1 day before the occurrence of the earthquake, but we could not detect anomalous strain changes exceeding 1×10⁻⁸ before the earthquake.  相似文献   

Zonal variations in abundance and body length of chaetognaths in the 140°E seasonal ice zone during the austral summer of 2001/02     

Makoto Terazaki  Kunio T. Takahashi  Tsuneo Odate 《Polar Science》2013,7(1):39-47

Time-series observations of chaetognaths were carried out during four cruises along the 140°E transect between 61°S and 66°28′S from November to March in the 2001/02 austral summer. Three species – Eukrohnia hamata, Sagitta gazellae and Sagitta marri – occurred in the samples between 0 and 150 m. E. hamata was the most dominant species comprising between 89.6 and 100% of the chaetognath population, followed by S. gazellae (0–5.7%). There were large differences in the abundance and size frequency distribution of body length of E. hamata between the north and south of the Southern Boundary of the Antarctic Circumpolar Current (SB-ACC) which was located between 64°S and 65°S. For E. hamata, low abundance and large sized animals (22–24 mm) occurred south of the SB-ACC. A possible reason could be that the breeding season in waters north of the SB-ACC may be early spring and summer. On the other hand, low reproduction was recognized by low the abundance of E. hamata and few occurrences of juveniles south of the SB-ACC (65°S). The result of a general comparison suggests that the abundance of chaetognaths along the 140°E transect has decreased during the 20 years since 1983.  相似文献